I have a Stevens Model 94 12 gauge, and I have fired shells ranging from dove loads to Winchester OO buck through it. The heaviest load I have fired in it is Federal Premium 1 5/8 oz #6. Around here that would be considered a turkey load, although it doesn't say "turkey" on the box. I have killed 4 legged predators after my chickens using that load and the Stevens.
At one time that was my only shotgun, but now the old girl has been semi-retired and serves as my barn gun. I keep some low base #6 one ounce shells close by it, just in case.
I hope you get a turkey in memory of your late great-uncle. Good luck!